Hurricane warnings issued for Florida as Isaac lashes Haiti

Those considered most vulnerable were urged to move into an evacuation camp housed in a school building, but others with nowhere else to go were digging trenches to avoid the water. Haiti's population remains especially vulnerable due to the country's sprawling shanty towns. NBC's Mark Potter reports.

By NBC News staff and wire services

Updated at 7:40 a.m. ET: Tropical Storm Isaac dumped heavy rains on Haiti on Saturday, threatening floods and mudslides in a country where hundreds of thousands of people remain homeless more than two years after a devastating earthquake.

Lashing rains and high winds were reported along parts of Haiti's southern coast and in the Haitian capital of Port-au-Prince, where more than 350,000 survivors of the 2010 earthquake are still living in fragile tent and tarpaulin camps.

Intermittent power outages affected the greater Port-au-Prince area in the early hours of Saturday as Isaac bore down on the impoverished Caribbean country.

At 5 a.m. ET, the U.S. National Hurricane Center issued a hurricane warning for the Florida Keys, including the Dry Tortugas, the west coast of Florida from Bonita Beach southward and Florida Bay.

It also issued a hurricane watch notice for Florida’s east coast from Golden Beach southward.

The NHC also said the Bahamas government had issued a hurricane watch for Andros Island.

The NHC's notice at 5 a.m. said Isaac had maximum sustained winds of 60 mph, down from 70 mph earlier Saturday, and was about 150 miles southeast of Guantanamo, Cuba.

'Life-threatening flash floods'The Weather Channel reported that bands of heavy rain triggered flooding in Puerto Rico through Friday, even with Isaac's center well to the southwest. A bridge collapse and mudslide was reported early Friday. Power outages were also reported. The U.S. Virgin Islands were also affected.

The Weather Channel said heavy rainbands on the cyclone's eastern flank were expected to continue to hammer Haiti and the Dominican Republic.

Storm total rainfall of 8 to 12 inches is possible, with up to 20 inches locally, The Weather Channel said. Additionally, 4- to 8-inches of rainfall, with isolated incidents of 12 inches, was possible in Jamaica.

"Life-threatening flash floods and mudslides will likely result from that amount of rain," it warned.

Isaac's march across the Caribbean comes as U.S. Republicans prepare to gather in Tampa, on Florida's central Gulf Coast, for Monday's start of their national convention ahead of the November presidential election.

The convention is still expected to proceed as planned but Gulf of Mexico operators began shutting down offshore oil and gas rigs on Friday ahead of the storm.

But the biggest immediate concern was heavily deforested Haiti.

With nearly 400,000 people still living in evacuation tents, a hurricane or even a tropical storm could lead to deaths and more damage to the already fragile country. NBC's Mark Potter reports.

On Friday, the government and aid groups evacuated thousands of tent camp dwellers but many Haitians chose to remain in their flimsy, makeshift homes, apparently out of fear they will be robbed, said Bradley Mellicker, head of disaster management for the International Organization for Migration (IOM).

"There's a lot of people who are resisting because they are scared of losing what little they have now," Mellicker said.

Churches, schools are sheltersAbout 3,000 volunteers from the government's Civil Protection office were dispatched across Haiti, warning people about flood and landslide risks, and about 1,250 shelters -- schools, churches or other community buildings -- that have opened their doors to house people seeking refuge from the storm.

But Red Cross officials said the number of shelters could be grossly inadequate and Prime Minister Laurent Lamothe acknowledged Haiti had "limited means" to ensure public safety.

Red Cross and IOM representatives joined government officials in trying to evacuate 8,000 of the "most vulnerable people," including 2,500 sick and disabled, from 18 tent camps in low-lying coastal areas of Port-au-Prince.

Many Haitians, most of whom scrape by on less than $1 per day, consider disaster an inevitable part of life in the poorest country in the Americas.

"We live under tents. If there's too much rain and wind, water comes in. There's nothing we can do," said Nicholas Absolouis, an unemployed 34-year-old mechanic at one camp for homeless people on the northern edge of the chaotic capital.

"There are still too many people living in the camps. There's a good chance that those might be destroyed with the passage of the cyclone," said France Hurtubise of the International Federation of Red Cross and Red Crescent Societies in Haiti.

Flooding could also help reignite a cholera epidemic, which has killed more than 7,500 people in Haiti since the disease first appeared in October 2010, foreign aid workers said.

Could hit New OrleansOn its current path, forecasters said Isaac would hit Cuba and the southern tip of Florida before making landfall anywhere from the Florida Panhandle in the northwestern part of the state to Alabama and as far west as New Orleans.

A tropical storm warning was issued for the entire coast of south Florida on Friday, and a hurricane warning also went into effect in the Florida Keys.

Party leaders are going ahead with their plans to host the Republican Convention in Florida, but GOP and Tampa officials have not ruled out the possibility of postponing the event if the storm poses a public safety risk. NBC's Kerry Sanders reports.

Isaac has drawn especially close scrutiny because of the Republican Party's convention, a four-day meeting during which former Massachusetts Governor Mitt Romney will receive the party's presidential nomination.

Party officials insist the convention will go ahead, even if they have to alter the schedule. But NHC meteorologist Rick Danielson said Tampa could potentially be hit by coastal flooding and driving winds or rain.

"There is still a full range of possible impacts on Tampa at this point," he said.

Danielson said it was very hard to project intensity before Isaac passes over mountainous Cuba on Saturday and Sunday and enters the Florida Straits. But the Florida Keys, the island chain off the southernmost part of the state, were definitely in harm's way.